Rifles which comprise a spring of the type described by EP 0655598 are spring rifles, which unlike those of the PCP (Pre-Charged Pneumatic) type, do not require an external source of compressed gas in order to fire a pellet or any type of ammunition.
In spring rifles manual compression of air is achieved by means of a spring. Consequently, the action of the trigger (firing) releases a spring which drives a piston. The rapid movement of the piston causes the compression of air in a reservoir. The compressed air contained in the reservoir or caused by the action of the piston is later evacuated through an opening of a smaller diameter than the reservoir, which facilitates the increase in air pressure. Finally, the evacuated compressed air is used to impel a pellet or any other type of ammunition.
Said rifles have rather lower performance in terms of accuracy compared to PCP type rifles. Principally, the difference in performance is due to the necessity of movement of parts in the firing which causes vibrations and recoil. Nevertheless, spring rifles are an important option owing to their low cost and because few additional accessories, such as pre-compressed gas cylinders, among others, are required.
At present, spring rifles possess mechanical firing by means of a ratchet mechanism and counter-ratchet which are uncoupled by the action of the trigger, allowing the passage of air, compressed by the spring, through the barrel.
In order to improve accuracy, it is necessary that the action of the user on the trigger should require the least possible force, as an action of greater force on the trigger causes an undesirable movement in the rifle at the time of firing. Therefore, at present, the coupling between the ratchet mechanism and counter-ratchet is made to have as small a contact area as possible. It is thus guaranteed that the movement required in order to displace the counter-ratchet and therefore fire is small, requiring a force of less magnitude for its operation.
This type of mechanism to reduce the amount of force necessary to activate the firing means that, when the contact surfaces become very small, any force applied externally, for example an impact, even if not effected direct on the trigger, causes the ratchet mechanism and the counter-ratchet to become uncoupled, causing unintentional firing. Therefore the necessity is observed of having the gentlest possible firing in a weapon which passes the safety tests such as for example the so-called drop test. This test consists of freely dropping the weapon in all possible positions of the rifle, this test is passed if the rifle does not fire in any of the positions.